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Monday, January 6, 2014

Q-tip anyone?

By Dana Sackett

You may have come across a video or two (or ten) of sharks munching down on dead whales and it’s easy to understand how a few sharks may get excited over encountering all that easily acquired energy-rich blubber. However, sharks are not the only ones that can benefit from these large dead mammals. Scientists can benefit too, but less so from their blubber than from their earwax. Now your initial reaction may be, “eww” but this is a true boon for scientists; especially because recent finding show how plugs of earwax can tell us about the whale’s lifetime exposure to pollution and more.

Scientists have routinely used plugs of whale earwax to determine a whale’s age. This process is possible because earwax is laid down seasonally in layers that occilate between dark and light each representing 6 months of life; dark during the feeding season and light during the fasting season when whales migrate.

Recently, however, scientist have discovered that whale earwax is even more useful than they originally thought because pollutants in the whales body are archived with each new layer of fat and wax that is laid down in their ear. With this new discovery scientists can determine which pollutants the whale had been exposed to over its lifetime and at what age it was exposed.

This diagram shows an earplug in a blue whale skull. The bacon-like image (D) is a close-up of the earplug. Images courtesy Michelle Berman-Kowalewskic, Santa Barbara Museum of Natural History. Source

In the recent groundbreaking study that discovered this new method the authors sampled a 10in long plug of earwax (panel B in the picture above) from an endangered blue whale that was hit by a ship off the coast of California in 2007. The results showed that the male was approximately 12 years old and had been exposed to high levels of persistent organic pollutants (like DDT) and pesticides in the first 6 months of life; likely passed on from the mother in the womb and though nursing. Many marine mammals have been known to pass contaminants built-up over time to offspring, with the highest concentrations going to the first born. This whale accumulated 20% of its lifetime burden from its mother.

The male blue whale whose earwax was used in the discussed study. Source

Mercury was also noted to show high spikes in years 5 and 10 and the authors suggested that these spikes may coincide with migration that brought the whale close to the west coast of the US where contamination would have been higher than in the open ocean or along other less polluted land masses.

Even more, contaminants are not the only chemicals recorded in these massive earplugs, hormones are also sequestered in the wax. Increased testosterone, in the blue whale mentioned above, suggested that he reached sexual maturity around 10 years of age. This increase also coincided with an increase in stress hormones, which could be linked to the stress of finding or fighting for a mate among much larger and older males.

The earplug from a female bowhead whale extracted in 1964. Analyzing earwax from older samples will help show how contaminant levels have changed in our oceans over time. Source

With super earwax that can record so much information over the lifetime of an animal and even provide information on the general health of our oceans, I am tempted to skip the “eww” factor and move on to “oooo” ….. for whale earwax at least.

Yordy JE, Wells RS, Balmer BC, Schwacke LH, Rowles TK, Kucklick JR. 2010. Life history as a source of variation for persistent organic pollutant (POP) patterns in a community of common bottlenose dolphins (Tursiops truncates) resident to Sarasota Bay, FL. Science of the Total Environment 408:2163-2172.